The present invention relates to a method for producing a pack for groups of products and to a machine for implementing said method, in particular, but without limiting the scope of the invention, for kitchen and/or toilet rolls.
In particular, this text focuses on bagging machines normally used for overwrapping a predetermined number of groups of products already packaged in plastic film, although this does not limit the scope of the invention, since the groups of products may also be pluralities or batches of loose products.
These groups of products are grouped together in predetermined batch configurations then fed, one after another, into a tubular packaging film wrapper.
These bagging machines, which usually form a final station of machines for producing the above-mentioned groups of products, bag the groups of products in tubular wrappers automatically formed by the bagging machine on the products to be overwrapped.
In practice, the machine forms the wrapper starting with a flat strip of packaging material film (fed from a reel positioned below a surface for movement of the groups of products). The strip of film is gradually folded over itself by special folder elements, forming a tube, supported from the inside of the wrapper being formed by suitable supporting elements (so that it forms a “tunnel” with a quadrangular cross-section), and having the longitudinal edges drawn near and overlapping one another.
There are also first sealing means positioned in front of the wrapper and the folder elements, angled transversally to the tubular shape, which then allow the wrapper to be sealed transversally to form, in sequence, a closed front end and a closed rear end.
Finally, second sealing means, angled longitudinally to the wrapper and opposite the longitudinal edges, close the tubular wrapper longitudinally to completely close the overwrap.
Basically, the process for forming the overwrap on the groups of products comprises the following steps:                forming the overwrap with the film around the folders and the supporting elements;        first seal at the front of the overwrap film;        insertion in the channel formed by the folders of a predetermined number of product groups, until they make contact with the closed front end of the wrapper;        further feeding of the product groups beyond the transversal sealers, simultaneously feeding the film from the reel thanks to the pushing motion of the products, and formation of the overwrap, gradually as the closed front end is fed along the machine together with the products inserted;        simultaneously with the formation of the overwrap the overlapping edges of film are longitudinally sealed by the second sealing means;        further activation of the first, transversal sealing means designed to close the overwrap wrapper at the rear of the products already bagged;        cutting to separate the bag obtained in this way from the rest of the film, using cutting means, thus starting a new and subsequent bagging cycle for the product groups.        
However, the machine structured in this way and the related operating cycle have disadvantages due to:                rather lengthy times required for overwrapping which, at present, sets an operating limit for all of the stations upstream of the bagging machine, which, over time, have been improved in terms of product quality and operating times; and        relatively low strength of the front seal at the current operating speeds.        
In particular, on the current bagging machine the point on which such problems are focused is the sealing speed, in particular on the front transversal sealing speed.
The film sealing is a time T divided into two separate operating sub-times, that is to say, the film melting time T1 and the seal cooling time T2: where the time T1 for melting the material is relatively low, whilst the cooling time T2 is relatively long, since the quality and strength of the seal is increased only after cooling.
Consequently, with the current cycle and with a transversal sealer fixed in a position, the front sealing times have to be observed in order to prevent the overwrap from breaking above all when the product groups fed forward come into contact with the front seal. As already indicated, product feed results in subsequent development of the overwrap.